; HI collisional ionization rate from Hui and Gnedin

function hici_hui, T

  T_HI = 1.57807d5
  lam  = 2.0d0 * T_HI / T

  rate = 21.11d0 * lam^(-1.089d0) / $
         ( 1.d0 + (lam/0.354d0)^(0.874d0))^(1.101d0)

  rate = rate * exp(-0.5d0*lam)

  rate = rate * T^(-3./2)

  return, rate

end
